This invention relates to an engine for an outboard motor and more particularly to an improved lubricating system for a four-cycle, outboard motor engine.
Two-cycle internal combustion engines have been frequently used as the prime mover for an outboard motor. The reason for the use of two-cycle engines is because of their compact nature and their high specific output. These features are particularly important in an outboard motor due to the very compact nature of such a propulsion device.
However, with increasing concerns about environmental protection, there has been a growing interest in the application of four-cycle engines for many applications that previously utilized two-cycle engines because of their aforenoted advantages. One of the advantages of four-cycle engines over two-cycle engines is also a feature that gives some disadvantages in connection with outboard motor application.
With two-cycle engines, the lubricating oil for the engine is generally consumed during engine running. That is, although two-cycle engines may use direct lubricating systems, the oil used for lubrication nevertheless is consumed during engine operation and any residual amounts is discharged to the atmosphere. This obviously has some environmental problems.
However, the recycled lubricating system utilized commonly with four-cycle engines presents some problems in application to outboard motors. That is, it is necessary to provide not only an oil reservoir, but also a system for circulating the oil to the various components of the engine to be lubricated.
Due to the fact that the exhaust gases are discharged from the engine through an exhaust system that is formed primarily within the drive shaft housing and lower unit of the outboard motor, it is sometimes difficult to isolate the oil reservoir for the engine from the exhaust system.
It is, therefore, a principal object of this invention to provide an improved lubricating system for a four-cycle engine utilized in an outboard motor.
It is a further object of this invention to provide an oil lubricating system for an outboard motor having a four-cycle engine wherein the lubricant for the engine is circulated in such a way so as to maintain adequate cooling for it.
In order to maintain simplicity of the engine and low cost, particularly in small displacements, resort may be had to splash lubricating system. Where splash lubricating systems are employed and the engine employs overhead valves to obtain better performance, it is necessary to deliver the lubricant to the cylinder head area for lubricating the valve actuating mechanism. This oil then must be returned to the reservoir. Because of this flow path, there increases the likelihood that the oil may be positioned in proximity to the exhaust system of the engine. It is, therefore, a still further object of this invention to provide an oil return system for an overhead valve four-cycle engine wherein the returned oil is also cooled.